1. Field of the Invention
This invention relates to variable focus spectacles and, in particular, it relates to an actuation mechanism for simultaneously adjusting the optical powers of each of the two lens units in a pair of variable focus spectacles.
2. Description of the Related Art
Variable focus spectacles are spectacles with adjustable optical power (i.e., adjustable focal length) in one or both lens units. Various mechanisms for changing the focal length of variable focus spectacles have been disclosed. For example, U.S. Pat. Nos. 5,138,494, 5,371,629 and 5,668,620 describe a variable focal length lens, for use in spectacles, which includes one or two rigid lenses to provide the wearer's distance correction, and a liquid filled lens bounded by a distensible elastomeric membrane to provide a variable optical power. The liquid, which has a fixed volume, is stored in the field of view between the elastomeric membrane and one of the rigid lenses. Variation of the optical power of the liquid filled lens is achieved by displacement of the outer periphery of the stretched elastomeric membrane or a membrane support or other parts.
U.S. Pat. No. 7,866,816 describes variable focus spectacles which comprise i) a focus module that includes two variable focus lens sections, said sections each including a first fixed lens and an adjustable focus liquid lens, and ii) a second fixed lens that preferably includes most or all of the optical power needed by the intended wearer to correct his/her distance vision. The second fixed lens is preferably attached to the focus module by magnetic attraction.
U.S. Pat. No. 6,053,610 describes an actuating mechanism for spectacles which include two variable focal length lens units. Each lens unit is fitted with a coupling member which extends from the lens unit into the bridge of the spectacles. A linearly-movable finger-operated slider, having a finger pad extending above the bridge, causes a cam within the bridge to pivot as it is moved, the cam being coupled to the coupling members causing them to move and the focal length of the lens units thereby to change.
U.S. Pat. No. 7,008,054 describes an actuating mechanism for spectacles which include two variable focus lens units. The mechanism mounts on the spectacle bridge; and includes two elongated drive levers mounted near opposite ends of the bridge, each extending toward the other end of the bridge. The free end of each driving lever is connected to its corresponding lens unit through a linkage. The driving levers are caused to rotate simultaneously, but in opposite directions, by a cam that is driven by a sliding member that slides along the bridge. By positioning the sliding member as desired, the spectacles wearer causes the cam to rotate, thereby causing the driving levers to rotate, and both lens units to change focal length. This actuation mechanism enables simultaneously controlling the optical powers of both lend units of the spectacles.